1. Field of the Invention
The present invention relates to an organic electroluminescent device, and more particularly, to an organic electroluminescent device using a mixture of high and low molecular light-emitting substances as a light-emitting substance so as to enable laser induced thermal imaging (LITI) as a high molecular organic electroluminescent device using a high molecular material emitting light under an electric field.
2. Description of Related Art
Generally, an organic electroluminescent device consists of various layers including an anode and cathode, a hole injection layer, a hole transport layer, a light-emitting layer, and an electron transport layer. The organic electroluminescent device is divided into high and low molecular organic electroluminescent devices depending on a material to be used, wherein each layer is introduced by vacuum deposition in the case of the low molecular organic electroluminescent (hereinafter referred to as EL) device while a light-emitting device is fabricated using a spin coating process, or an ink jet process in the case of the high molecular organic EL device. In the case of a single color device, an organic EL device using a high molecular material is simply fabricated using the spin coating process, wherein the organic EL device using a high molecular material has drawbacks of lower efficiency and life cycle, although it has a lower driving voltage compared to an organic EL device using a low molecular material. Furthermore, red, green and blue color high molecular materials should be patterned when fabricating a full color device, and the organic EL device using high molecular materials has problems in that emitting characteristics such as efficiency and life cycle are deteriorated when using ink jet technology or laser induced thermal imaging.
Particularly, in the case of most materials, a single material is not transferred when patterning the material by using laser induced thermal imaging. A method of forming patterns of an organic EL device by laser induced thermal imaging is disclosed in Korean Patent No. 1998-51814, and U.S. Pat. Nos. 5,998,085, 6,214,520 and 6,114,088.
In order to apply the heat transfer process, a light source, a transfer film and a substrate are needed at the least, and light coming out of the light source is absorbed by a light absorption layer of the transfer film to be converted into heat energy so that a transfer layer forming material of the transfer film is transferred onto the substrate by heat energy to form a desired image, as disclosed in U.S. Pat. Nos. 5,220,348, 5,256,506, 5,278,023 and 5,308,737.
The heat transfer process can be used to fabricate a color filter for liquid crystal display devices, or to form patterns of a light-emitting substance, as disclosed in U.S. Pat. No. 5,998,085. Although it is written in U.S. Pat. No. 5,998,085 that a light-emitting substance for an organic EL device is transferred onto a substrate, characteristics on materials used to improve transfer properties are not mentioned in the patent.
Furthermore, although there are such patents as U.S. Pat. No. 6,117,567 for creating other colors using phase separation of light-emitting substances, Korean Patent No. 2001-3986 for increasing efficiency, or U.S. Pat. No. 5,965,281 for improving device characteristics by adding ionic surfactants, all of the patents are related to improvement of characteristics of materials themselves. Therefore, literature and patents regarding improvement of high molecular materials during patterning using laser induced thermal imaging do not exist currently.